Only another anecdotal story --
My best personal example of "herd immunity" is a large independent living apartment facility (maybe 250 elderly residents) that I frequent because a cousin lives there, doesn't have any immediate family that cares for her, and I'm also her medical POA. Of course last year, before availability of vaccines, the facility locked down as a preventive measure, I think it locked down effective April 1, 2020, with nobody in or out except staff and medical providers. Residents were essentially confined to their rooms, meals were delivered, transportation was provided to medical facilities when needed, etc. Any time a resident left and returned to the facility, they were quarantined for 2 weeks (confined to room, no visitors except staff). Masks were required for all residents anytime outside of their room for any reason and within their room if anyone else present, all staff all the time, and for any visitors after visitor restrictions were eased in late 2020. Visitors had additional restrictions, had medical questions to answer, and temperature checked at front desk. Visitors passed thru common areas, but could only visit in individual rooms of those residents not otherwise quarantined. Of course, under their lock-down, quarantine wasn't much different than just being under lock-down anyway, except that if not under quarantine, they could receive approved visitors. I don't recall (and maybe never knew) how many residents were infected, nor how many died during the lock-down, which essentially lasted until May 1, 2021. I do know they had a vaccination program as soon as it was available to them, and they reported that over 95% of residents and staff were vaccinated, mostly the 2-shot Pfizer jabs. In the meantime, they had a regular testing program, though think only non-vaccinated, a sample of those vaccinated, and all previously positive-test residents underwent regular testing. They only lifted the lock-down after no residents nor staff tested positive for 2 full weeks, and it took until May 1, 2021, to get to that point. After the lock-down ended, mask requirements remained in effect, and visitor restrictions remained in effect, yet their common activities resumed, dining hall opened, residents could leave and return without quarantine, etc.
In June, 2021, after having gone off lock-down for only slightly over a month, there was 1 staff member (don't know if they were vaccinated or not) that became ill, was tested, and tested positive. This initiated another immediate round of testing at the facility, with subsequent identification of additional positives, and another lock-down. Even though the facility reported over 95% vaccination rate, during the 2 weeks following when 1 staff member became ill, there were 13-14 more employees that tested positive, plus 68-69 residents. I think there were 5 resident deaths in this latest outbreak, all of them vaccinated, but obviously elderly. During this lock-down, they tested every single staff member and resident once a week, whether vaccinated or not, and kept the lock-down until there were zero positive tests for 2 consecutive weeks. The lock-down just ended September 1st, though some visitor restrictions still apply.
Bottom-line -- I don't really think there is any such thing as "herd immunity" for Covid. The vaccinations do not prevent the disease, though they do appear to lessen the impact or severity. As evidenced by how quickly the 2021 summer round of Covid spread within that facility, masks really don't do much, if anything, to stop the spread.
My cousin is only 76, but has been Stage 4 kidney disease for a few years, refuses dialysis, weighs less than 85 pounds, and has been hospitalized for at least a week (2 weeks in April this year) every year for past 7-8 years. She received the Pfizer shots as soon as they were available, only wears a mask when required to do so, and has never tested positive for Covid.
